With the Warder's Beacon lit, the Magistrate and Resistance are drawn into another battle over ancient relics, soon drawing the attention of the owner of said relics, as well as other less welcome company.
Story
The entire Realm could see it, the Warder's Beacon had been lit, a call to action for the Warders, that the Realm needed their help once again. However, the Warders were long gone, having mysteriously vanished at some point, leaving no one to answer the call.
However, as the beacon remained lit, the ancient power being shown to the Realm, the Magistrate and Resistance, like moths to the flame, were drawn towards the island in the hopes of claiming this power for themselves, likely in hopes of using it to win the Crystal War. The Resistance arrived first, followed shortly by the Magistrate, and with the two sides meeting, the outcome was certain, yet another battle between the two.
Following this, the Resistance managed to secure victory and claim the Warder's relics for themselves, though the celebration would be short lived. Drawn to them by the power of the gauntlets they carried, the group was attacked by Judd Roberts, also known as Admiral Dredge, the most feared pirate of the Eight Oceans. None could hope to match his might on the open waters, and so he easily stole the gauntlets from the group.
However, when Judd attempted to use the gauntlets to control a Warder Dragon, as a Warder's ability to command dragons stems from the dragon's own willingness to listen and trust the Warders, qualities Judd lacked due to not being a Warder, the dragon instead attacked the pirate, easily defeating him and sending him sinking into the dark ocean depths. But this was not the end of the pirate, as deep below the waves, Judd encountered the Abyssal Lord Dredge, who brought him back as Dredge, Admiral of the Abyss. He would once again reclaim the gauntlets before docking at his hideout of Marauder's Port.
Soon after, though, Dredge would receive an unwanted visitor; while thought completely gone, one Warder remained, Imani, who arrived at Marauder's to take back her gauntlets. She easily defeated Dredge and reclaimed her gauntlets.
Sources
This information comes from the Dragon's Call event video, the Dark Tides lore cinematic, Imani's bio and teaser trailer (all linked below), the various Trial of the Realm descriptions for Warder's Watch, this stream, this dev statement, and the Fight of the Shattered Desert story.
Gallery
Dragon's Call
Welcome to Warder's Watch, the former home of the ancient group. 
It was thanks to their efforts the ancient dragons were subdued and the Realm could become peaceful. 
But now with the ongoing Crystal War... 
...and the beacon being lit, the group is needed once more to restore peace.
Dark Tides
Following the battle, the Resistance emerges victorious against the Magistrate. With this victory, the group has claimed a pair of Warder gauntlets. Because of its power though, it attracts unwanted attention. Judd Roberts, or Admiral Dredge, the most feared pirate of the Eight Oceans, easily steals the gauntlets from them. Sensing Judd taking possession of the gauntlets and deeming him unworthy... ...the dragon attacks the pirate. Easily defeated, Judd sinks below the waves. But death is not what awaited the pirate. Reborn through the Abyss, the pirate sails again. Dredge, Admiral of the Abyss, would not be denied his treasure.
Imani's Return
Imani easily defeats Dredge and reclaims her gauntlets. Now, she seeks those responsible for lighting the Warder's Beacon.
Videos